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Lichen-derived monoaromatic compounds are bioactive compounds, associated with various pharmacological properties: antioxidant, antifungal, antiviral, cytotoxicity, and enzyme inhibition. However, little is known about data regarding alpha-glucosidase inhibition and antimicrobial activity. Very few compounds were reported to have these activities. In this paper, a series of monoaromatic compounds from a lichen source were isolated and structurally elucidated. They are 3,5-dihydroxybenzoic acid (<b>1</b>), 3,5-dihydroxybenzoate methyl (<b>2</b>), 3,5-dihydroxy-4-methylbenzoic acid (<b>3</b>), 3,5-dihydroxy-4-methoxylbenzoic acid (<b>4</b>), 3-hydroxyorcinol (<b>5</b>), atranol (<b>6</b>), and methyl hematommate (<b>7</b>). To obtain more derivatives, available compounds from the previous reports such as methyl β-orsellinate (<b>8</b>), methyl orsellinate (<b>9</b>), and D-montagnetol (<b>10</b>) were selected for bromination. Electrophilic bromination was applied to <b>8</b>–<b>10</b> using NaBr/H₂O₂ reagents to yield products methyl 5-bromo-β-orsellinate (<b>8a</b>), methyl 3,5-dibromo-orsellinate (<b>9a</b>), 3-bromo-D-montagnetol (<b>10a</b>), and 3,5-dibromo-D-montagnetol (<b>10b</b>). Compounds were evaluated for alpha-glucosidase inhibition and antimicrobial activity against antibiotic-resistant, pathogenic bacteria <i>Enterococcus faecium</i>, <i>Staphylococcus aureus</i>, and <i>Acinetobacter baumannii</i>. Compound <b>4</b> showed stronger alpha-glucosidase inhibition than others with an IC₅₀ value of 24.0 µg/mL. Synthetic compound <b>9a</b> exhibited remarkable activity against <i>Staphylococcus aureus</i> with a MIC value of 4 µg/mL. Molecular docking studies were performed to confirm the consistency between in vitro and in silico studies.